In browsers, there is a limit on the number of simultaneous HTTP connections for the same domain. This limit ensures that a website does not consume excessive network resources when downloading assets, thereby maintaining network fairness and efficiency.
In the early HTTP/1.1 protocol, according to RFC2616, browsers should limit parallel connections for the same domain to 2. However, this limit appears overly conservative today, given the more advanced network environments compared to the past.
As time has progressed, modern browsers have expanded this limit to improve page load speed and user experience. For example:
- Google Chrome and Safari: approximately 6 parallel connections.
- Firefox: also approximately 6.
- Internet Explorer 11: up to 8 parallel connections.
- Microsoft Edge: approximately 6 to 8.
Notably, with the widespread adoption of HTTP/2, this issue has become less prominent. HTTP/2 supports multiplexing, allowing requests and responses to be sent in parallel over a single connection, reducing the number of connections needed and significantly improving efficiency. Consequently, in HTTP/2 environments, a single connection can handle numerous parallel requests, making the browser's limit on domain-specific parallel connections less critical.
In summary, different browsers and protocols have varying limits on parallel connections, but modern browsers generally range from 6 to 8. With the increasing adoption of HTTP/2, the traditional parallel connection limit is gradually losing its importance.